This invention relates to the field of surface controlled subsurface safety systems for use in wells producing hydrocarbons.
Perhaps the earliest surface controlled subsurface safety valve system is disclosed in Knox U.S. Pat. No. 2,518,795. Numerous improvements have occurred since that time, but certain problems have remained. In general, well operators have desired a full opening surface controlled subsurface safety valve that can be easily replaced upon failure. These two criteria in the past have led to differing patterns of development which have not been resolved until the present invention.
To achieve the easily replaceable feature, through the tubing bore movable or wireline installed and retrievable surface controlled subsurface safety valve have been developed. See, for example, the following United States Patents:
______________________________________ 3,078,923 3,157,233 3,642,070 3,675,720 3,747,682 3,763,933 ______________________________________
While those subsurface safety valves had the advantage of easy replacement, they did severely restrict flow through the subsurface safety valve. This not only limited production but often caused flow erosion of the tubing above the valve. This problem was partially solved by my development of a larger diameter ball element as disclosed and claimed in U.S. Pat. No. 3,870,102. Another drawback was the need to remove these valves in order to conduct well servicing operations below the valve.
Full opening subsurface valves, i.e., valves having a flow opening through valve housing substantially equal to the well tubing bore possessed neither of these drawbacks. Flow erosion is reduced and no restriction is presented to running other well tools through the valve when in the open position to perform various operations below the valve. For example, see Keithahn U.S. Pat. No. 2,998,077.
To achieve the full opening, it was necessary to run a tubing retrievable type valve (i.e. retrievable with the tubing from the well) and which formed a portion of the well tubing. This frequently required a larger, expensive casing program to provide clearance for the enlarged outer diameter of the valve housing. In addition, this presented the problem of pulling the entire well tubing string which necessitated killing the well with possible permanent damage to the hydrocarbon producing formation. Since the entire tubing string was required to be supported and manipulated for releasing any packers or other downhole seals and then reinstalling same, expensive workover rigs were required to replace tubing retrievable safety valves.
In weighing the business risks, the operators have tended to prefer wireline retrievable surface controlled subsurface valves. However, the capability of installing a wireline retrievable valve in a tubing retrievable valve, such as disclosed in my patent application Ser. No. 072,034, filed Sept. 14, 1970 (now abandoned after filing continuation application Ser. No. 256,194, filed May 23, 1972 and now offered the compromise of installing a wireline retrievable valve in a locked open tubing retrievable valve. This concept was further refined in Mott U.S. Pat. No. 3,744,564 which disclosed that when tubing retrievable valve failure occurred a wireline retrievable valve could be installed and operated by the controls of the tubing retrievable valve.
Another concept of using a full opening tubing retrievable valve is retrieving only the portion of the tubing above the safety valve. Examples of such concept are found in the following U.S. Pats.:
U.S. Pat. No. 3,842,913 PA1 U.S. Pat. No. 3,870,104 PA1 U.S. Pat. No. 3,844,346
A drawback to such concept was that it required the well to be cased and completed in a manner that limited the well operator's flexibility in maintaining the well.
A similar arrangement has been the installation of a full opening surface controlled subsurface safety valve in a tubing hanger suspended below the mudline. For example, see Crowe U.S. Pat. No. 3,771,603, which discloses such a tubing hanger with the full opening surface controlled subsurface safety valve installed in the tubing hanger.
These subsurface safety systems generally require the use of an installation tool for setting the tubing hanger which was followed by the installation of the subsurface safety valve. An example of such a running tool is disclosed in U.S. Pat. No. 4,067,388. Because of the necessity to "space out" during the second trip installation time was often lengthy with this equipment. Removal operations were the same in that the safety valve was removed by pulling the stinger of the valve from the tubing hanger and thereafter using a retrieving tool to retrieve the tubing hanger and the production tubing secured in the well below the tubing hanger. Such operations were very lengthy and as the workover equipment necessary to perform installation and retrieval is generally rented, such operations were extremely costly to the operator and therefore extremely undesirable.
The model TA tubing hanger anchor manufactured by Brown Oil Tools, Inc. enables the installation of a full opening subsurface safety valve in a single trip. The subsurface tubing hanger is hydraulically set and the setting mechanism remains exposed to well fluid pressure during production. This creates an additional risk of tubing leakage. In addition, the safety joint disposed in the tubing above the safety valve limited the weight of the equipment that could be installed on the single trip.
Despite such drawbacks, such tubing hanger systems are desirable in that the full opening valve may be retrieved and replace without the need for a workover rig. Offshore platforms are usually equipped with cranes and by proper location of the tubing hanger, the cranes could be used to lift the upper portion of the tubing to replace the safety valve. In view of the cost as well as availability of workover rigs, this was extremely desirable.